1. Field of the Invention
This invention relates to devices for locking cords against longitudinal movement generally, and more specifically to devices for retaining surgical cables under high tension, suitable for surgical implantation in a human body.
2. Description of the Related Art
Cable locks based on the principle of the wedge are known. Consider, for example, the lock described in U.S. Pat. No. 4,156,576. Such cable locks employ a wedge as a simple machine for securing cordage.
At high tensions, certain modern polymer based cords seem to defy all attempts to engage and lock the cord, dramatically curtailing their range of practical use. Several of the material properties of polymer fibers tend to complicate efforts to fasten polymer cords. The surfaces tend to be slippery; the materials have memory, which tends to unravel knots; and in some circumstances the materials tend to deform and flow (as implied by the common term “plastic” ). For these reasons, conventional knots are inadequate. Other clasps and fasteners tend to lose purchase in the cords, and under high tension the polymer cords tend to slip. Attempts to counteract slippage by application of increased pressure often result in cutting or fraying of the cord.
As disclosed in U.S. Pat. No. 6,589,246, certain polymer cables have shown promise for surgical use. However, their widespread acceptance depends in part on the availability of an efficient, economical, convenient and reliably means of clamping or retaining the cable under moderate to high tension.